Underground storage tank

Abstract

Storage tanks, for example, underground septic tanks, and their methods of fabrication are provided. The tanks include a substantially liquid impermeable plastic vessel having a top, a bottom, and sides; a concrete container encasing and retaining the plastic vessel, the concrete container contacting the bottom and at least partially contacting the sides of the plastic vessel; and at least one opening for receiving effluent, for example, waste effluent, into the plastic vessel. The methods of fabricating the tanks include positioning a plastic vessel into an enclosure; introducing concrete into the enclosure about the plastic vessel; allowing the fluid concrete to cure to provide a substantially solid concrete container about the plastic vessel; and removing the plastic vessel having a concrete container from the enclosure. Vessel shape retaining devices are also disclosed. Aspects of the invention are uniquely adapted to underground storage.

The invention claimed is: 
     
       1. A storage tank comprising:
 a substantially liquid impermeable, cylindrical plastic vessel having a top, a bottom, sides, and a substantially horizontal longitudinal axis; 
 a concrete container encasing and retaining the cylindrical plastic vessel, the concrete container contacting the bottom and at least partially contacting the sides of the cylindrical plastic vessel; and 
 at least one opening for receiving material into the cylindrical plastic vessel; 
 wherein the storage tank is adapted to withstand vehicle loading. 
 
     
     
       2. The storage tank as recited in  claim 1 , wherein the concrete container substantially completely contacts the sides of the vessel and at least partially contacts the top of the vessel. 
     
     
       3. The storage tank as recited in  claim 1 , wherein the cylindrical plastic vessel comprises a vessel made of high-density polyethylene (HDPE). 
     
     
       4. The storage tank as recited in  claim 1 , wherein the cylindrical plastic vessel comprises a substantially circular cylindrical vessel. 
     
     
       5. The storage tank as recited in  claim 1 , wherein the storage tank further comprises at least one opening for removing material from the plastic vessel. 
     
     
       6. The storage tank as recited in  claim 1 , wherein the substantially liquid impermeable plastic vessel comprises a plastic vessel substantially impermeable to ground water. 
     
     
       7. The storage tank as recited in  claim 1 , wherein the tank further comprises a plurality of ports. 
     
     
       8. The storage tank as recited in  claim 7 , wherein at least one of the plurality of ports comprises at least one conduit assembly adapted to one of direct material to the bottom of the vessel and extract material from the vessel. 
     
     
       9. The storage tank as recited in  claim 1 , wherein the substantially liquid impermeable plastic vessel comprises multiple plastic layers. 
     
     
       10. The storage tank as recited in  claim 9 , wherein the multiple plastic layers comprise an inner layer and an outer layer. 
     
     
       11. The storage tank as recited in  claim 9 , wherein the multiple plastic layers comprise an inner layer of high-density polyethylene and an outer layer of polyethylene. 
     
     
       12. The storage tank as recited in  claim 1 , wherein the substantially liquid impermeable plastic vessel comprises reinforcing structures molded into the plastic vessel. 
     
     
       13. The storage tank as recited in  claim 1 , wherein the cylindrical plastic vessel comprises a hollow container. 
     
     
       14. The storage tank as recited in  claim 1 , wherein the at least one opening for receiving material into the cylindrical plastic vessel comprises a first opening in a first end of the cylindrical plastic vessel, and wherein the storage tank further comprises at least one second opening in the second end of the cylindrical plastic vessel, opposite the first end. 
     
     
       15. The storage tank as recited in  claim 1 , wherein the concrete container substantially completely encases the cylindrical plastic vessel. 
     
     
       16. The storage tank as recited in  claim 1 , wherein the concrete container comprises an elongated cylindrical concrete container having a direction of elongation; and wherein the horizontal longitudinal axis of the cylindrical plastic vessel is in the same direction as the direction of elongation of the elongated cylindrical concrete container. 
     
     
       17. The storage tank as recited in  claim 16 , wherein the direction of elongation of the concrete container is substantially parallel to the plane of ground. 
     
     
       18. The storage tank as recited in  claim 1 , wherein the storage tank comprises an underground storage tank. 
     
     
       19. The storage tank as recited in  claim 1 , wherein the vehicle loading comprises at least AASHTO H-20 LL vehicle loading. 
     
     
       20. The storage tank as recited in  claim 1 , wherein the vehicle loading comprises at least AASHTO H-5 vehicle loading. 
     
     
       21. The storage tank as recited in  claim 1 , wherein the concrete container comprises a cylindrical concrete container. 
     
     
       22. The storage tank as recited in  claim 21 , wherein the cylindrical concrete container comprises one of a rectangular cylindrical concrete container and a circular cylindrical concrete container. 
     
     
       23. A storage tank comprising:
 a substantially liquid impermeable cylindrical plastic vessel comprising a hollow container having a top, a bottom, sides, and a substantially horizontal longitudinal axis, the substantially liquid impermeable cylindrical plastic vessel substantially preventing leakage into the tank and seepage from the tank; 
 a concrete container encasing and retaining the cylindrical plastic vessel, the concrete container substantially completely encasing the cylindrical plastic vessel, the concrete container having a mass to substantially prevent buoyant displacement of the tank and a structural strength sufficient to withstand traffic loading; and 
 at least one opening for receiving material into the cylindrical plastic vessel, the at least one opening comprising a first opening in a first end of the cylindrical plastic vessel, and at least one second opening in a second end of the cylindrical plastic vessel, opposite the first end; 
 wherein the storage tank is adapted to withstand vehicle loading; and 
 wherein the concrete container comprises an elongated cylindrical concrete container having a direction of elongation; and 
 wherein the horizontal longitudinal axis of the cylindrical plastic vessel is in the same direction as the direction of elongation of the elongated cylindrical concrete container and substantially parallel to the plane of ground. 
 
     
     
       24. The storage tank as recited in  claim 23 , wherein the storage tank comprises an underground storage tank. 
     
     
       25. The storage tank as recited in  claim 23 , wherein the elongated cylindrical concrete container comprises one of an elongated rectangular cylindrical concrete container and an elongated circular cylindrical concrete container.